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Math Help - Fluid Pressure problem.

  1. #1
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    Fluid Pressure problem.

    Hey all,


    I have this problem and I cannot for the life of me figure out what I'm doing wrong that the homework isn't accepting my answer. Can someone take a look at what I'm doing and maybe tell me whats wrong? Problem is below:


    A rectangular tank is wide and deep. If the tank is only half full with water, find the force against one end of the tank.
    (Recall that = .)


    F = ______wN




    Pressure on Strip: (6-y)w
    Area of Strip: 13dy
    Force against strip: (6-y)*13dy = 13w(6-y)dy


    F = Integral from 0-3 {13w(6-y)dy}

    13w(6y-y^2/2)dy


    13w(18-9/2)


    13(27/2) = 351/2

    I've tried entering my answer in as a decimal and as the exact answer and for some reason its telling me it is incorrect. Any help would be great.
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  2. #2
    MHF Contributor

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    Quote Originally Posted by matt1989 View Post
    Hey all,


    I have this problem and I cannot for the life of me figure out what I'm doing wrong that the homework isn't accepting my answer. Can someone take a look at what I'm doing and maybe tell me whats wrong? Problem is below:


    A rectangular tank is wide and deep. If the tank is only half full with water, find the force against one end of the tank.
    (Recall that = .)


    F = ______wN




    Pressure on Strip: (6-y)w
    Area of Strip: 13dy
    Force against strip: (6-y)*13dy = 13w(6-y)dy


    F = Integral from 0-3 {13w(6-y)dy}

    13w(6y-y^2/2)dy


    13w(18-9/2)


    13(27/2) = 351/2

    I've tried entering my answer in as a decimal and as the exact answer and for some reason its telling me it is incorrect. Any help would be great.
    Your method is excellent but w= 10000 seems to have disappeared from you answer! Try [b](351/2)(10000)= 1755000. Gosh, you weren't even close were you?
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  3. #3
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    Joined
    Nov 2009
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    well the reason why I didn't multiply the 351/2 by 10,000 is because they way you enter the answer you don't have to because they just have the w as part of the answer. Its just a little fill in the blank question and they don't make you multiply your answer by the density of water (10,000). Rather they just make you enter it as 351/2 wN.

    But I tried entering in 1755000 too and it still didn't work.

    That's why I was wondering if I had done something else wrong.
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